Efficient Inverse Isoparametric Mapping Algorithm for Whole Body Computed Tomography Registration Using Deformations Predicted by Nonlinear Finite Element Modeling

Abstract

Biomechanical modeling methods can be used to predict deformations for medical image registration and particularly, they are very effective for wholebody computed tomography (CT) image registration because differences between the source and target images caused by complex articulated motions and soft tissues deformations are very large. The biomechanicsbased image registration method needs to deform the source images using the deformation field predicted by finite element models (FEMs). In practice, the global and local coordinate systems are used in finite element analysis. This involves the transformation of coordinates from the global coordinate system to the local coordinate system when calculating the global coordinates of image voxels for warping images. In this paper, we present an efficient numerical inverse isoparametric mapping algorithm to calculate the local coordinates of arbitrary points within the eightnoded hexahedral finite element. Verification of the algorithm for a nonparallelepiped hexahedral element confirms its accuracy, fast convergence, and efficiency. The algorithm's application in warping of the wholebody CT using the deformation field predicted by means of a biomechanical FEM confirms its reliability in the context of wholebody CT registration.